ACID-BASE INDICATORS

These are some acid-base indicators.
They are substances that change their color depending on the acidity of the medium. They are used in Chemistry to do an experiment called acid-base titration.
When an indicator reacts with an acid, it is formed HIn+, the acid form of the indicator.
When an indicator reacts with a base, it is formed InOH-, the basic form of the indicator.
The acidic and basic forms have usually very different colors.
Fill seven small erlenmeyers with some acid.
And seven small erlenmeyers with some base.
Let's see the color changes.
Phenolphthalein in an acidic medium is colorless and in a basic medium it is pink.
This is neutral red.
Neutral red in an acidic medium is red and in a basic medium it is yellow.
This is Congo red.
Congo red in an acidic medium is violet and in a basic medium it is red.
This is methyl red.
Methyl red in an acidic medium is red and in a basic medium it is yellow.
This is gentian violet.
Gentian violet in acidic medium is yellow and in basic medium it is violet.
This is methylene blue.
Methylene blue in acidic medium is blue and in basic medium is violet.
This is a universal indicator.
The universal indicator in an acidic medium is red and in a basic medium it is blue or gray.
This is the rainbow of colors obtained with these seven acid-base indicators.

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